Honest biologists can’t tell you when human life begins

Honest biologists like Sahotra Sarkar, that is. Unfortunately, the people that pushed the Texas anti-choice law are liars for Jesus, not biologists at all.

A recent friend-of-the-court filing in that case implicitly claims that biology – and therefore biologists – can tell when human life begins. The filing then goes on to claim explicitly that a vast majority of biologists agree on which particular point in fetal development actually marks the beginning of a human life.

Neither of those claims is true.

There is no definitive single marker for the moment when a zygote becomes “human” — we can’t even define satisfactorily what humanity means, but one thing for sure, it’s not going to be discovered by molecular biologists. Maybe by philosophers or artists or writers or something, but I suspect that if you asked them, they’d all shrug and say they don’t know either.

As a developmental biologist, I’m satisfied with the idea that a human being emerges gradually from progressive interactions between cells and environment — it is not a unitary thing, and therefore doesn’t have a single discrete point of appearance. That’s been the position of informed scientists since roughly Aristotle.

That doesn’t stop the liars for Jesus from pretending that biology supports their claim.

The most recent high-profile example of this claim is in that amicus brief filed with the Supreme Court in the Mississippi case.

The brief, coordinated by a University of Chicago graduate student in comparative human development, Steven Andrew Jacobs, is based on a problematic piece of research Jacobs conducted. He now seeks to enter it into the public record to influence U.S. law.

First, Jacobs carried out a survey, supposedly representative of all Americans, by seeking potential participants on the Amazon Mechanical Turk crowdsourcing marketplace and accepting all 2,979 respondents who agreed to participate. He found that most of these respondents trust biologists over others – including religious leaders, voters, philosophers and Supreme Court justices – to determine when human life begins.

Then, he sent 62,469 biologists who could be identified from institutional faculty and researcher lists a separate survey, offering several options for when, biologically, human life might begin. He got 5,502 responses; 95% of those self-selected respondents said that life began at fertilization, when a sperm and egg merge to form a single-celled zygote.

That result is not a proper survey method and does not carry any statistical or scientific weight. It is like asking 100 people about their favorite sport, finding out that only the 37 football fans bothered to answer, and declaring that 100% of Americans love football.

In the end, just 70 of those 60,000-plus biologists supported Jacobs’ legal argument enough to sign the amicus brief, which makes a companion argument to the main case. That may well be because there is neither scientific consensus on the matter of when human life actually begins nor agreement that it is a question that biologists can answer using their science.

That is methodologically a terrible survey. I’d like to know the details of the question: the summary implies that they were given “options”…a multiple choice question? Was “This question is bullshit” one of the options? I think probably not. Just the idea of putting the question in the form of multiple choices or true/false limits the potential accuracy of the answer.

The bottom line is that ideas are being misrepresented by these supporters of abortion bans, and no, biologists cannot answer, or have a significantly more nuanced answer, than they want, so they are intentionally lying to the courts. Can we get ’em for perjury?

The overall point is that biology does not determine when human life begins. It is a question that can only be answered by appealing to our values, examining what we take to be human.

Perhaps biologists of the future will learn more. Until then, when human life begins during fetal developments is a question for philosophers and theologians. And policies based on an answer to that question will remain up to politicians – and judges.

Except, please, keep the theologians out of it. They’ve only got dogma, not evidence.


  1. Reginald Selkirk says

    There is no definitive single marker for the moment when a zygote becomes “human”…

    I see no hope for progress if the wrong language is being used. Of course the zygote is “human”. What do you expect, that it is canine or feline? Pre-fertilization, the egg and sperm were also “human.” The right question is when the zygote/fetus becomes a “person.”

  2. pick says

    I earned a BS in cell biology a long time ago so please correct this as necessary but I thought I learned that life began ~2 billion years ago and that the information has been passed from one generation to the next, (with modifications) ever since.
    Human life began something like ~15,000 – 20,000 years ago and likewise has been passed generation to the next with modification. I’m very vague on these numbers but I think this provides some perspective on the issue. I think your answer is appropriate in consideration of any individual human life.
    Developmental was my favorite course! It was team taught by a Botanist and Animal physiologist.

  3. Snarki, child of Loki says

    Need a new, better, survey.
    Similar questions, but add an option: “this is stupid, post-natal abortion should be performed on the anti-science assholes”.

  4. Pierce R. Butler says

    Reginald Selkirk @ # 1: The right question is when the zygote/fetus becomes a “person.”

    According to classical Christian doctrine for over a thousand years, not until baptism. Anyone who died before that point was not entitled even to burial in the official community cemetery.

  5. billseymour says

    This non-biologist’s understanding is that life doesn’t begin, it continues.

    When a zygote becomes a person with rights is an interesting question; but it’s an ethical and legal question, not a biological one.

    Also, IIRC, the bible sets that point at birth.  If that’s right, then these folks are lying, not only about what scientists say, but also about what they themselves say when they claim to adhere to biblical teachings.

  6. acroyear says

    Now the question comes – why didn’t a faculty advisor (if he’s a graduate student) review the methodology ahead of time and tell him it as garbage?

  7. raven says

    but I thought I learned that life began ~2 billion years ago

    Close. You are only 1.8 billion years off.

    The earliest evidence we have for life is 3.8 billion years ago. It’s been an unbroken chain between then and now for our entire biosphere.

  8. raven says

    Also, IIRC, the bible sets that point at birth.

    The bible sets the beginning of human life as 1 month after birth.

    This is common in many societies. In many African cultures, they don’t name a baby until three months after it is born. Because there is a high probability of a baby dying before then so they don’t want to get to attached to it.

    This was also true in the USA up until recently in parts of the USA. For the exact same reason.

  9. acroyear says

    @billseymour #6 “Also, IIRC, the bible sets that point at birth.”

    There are aspects that are taken out of context as implying otherwise, like Jerimiah’s “I knew you before I formed you in the womb; I set you apart for me before you were born” – these also, of course, also tie into pure Calvinism and predestination and from there the whole prosperity gospel crapola, which these same people also all embrace. But really the anti-abortion efforts within the Catholic church derived from that, and then the evangelicals embraced it post RvW as their way to garner support from Catholics to their current rise in power.

  10. Howard Brazee says

    Even the Bible doesn’t support their claim. (Unborn are not valued the same as people in the Bible)

    And tradition let the woman determine when embryos “quickened” into fetuses (although they didn’t use that term). But obviously women couldn’t be trusted to make such decisions.

    The abortion issue was created when Jim Jones University was not allowed to claim tax-exempt status while excluding blacks. It was all about political power.

    We see science denial for people who don’t want to wear masks or get inoculated. They’re all excuses.

    And they have guns because they like guns, not because they need them to fight tyrants. But the Constitution gives them an excuse.

  11. beer says

    Zygote -> Human is like the “Paradox of Heap”:

    At what point does a collection of sand grains become a “heap” of sand grains? When you add one more grain? Or two? Etc.

    It’s a heap/human at some point. But you’ll never be able to perfectly define where/when that is.

  12. stroppy says

    “Two million years of human evolution and this is what we get: you morons.”
    (from Dark Angel, responding to a mob of bigots.)

  13. nifty says

    I was one of the biologists who received an invitation to answer the survey. I indicated I thought it was stupid, and had to post a second response to adamantly indicate I did not support anything like the amicus brief.

  14. chigau (違う) says

    pick #2

    Human life began something like ~15,000 – 20,000 years ago…

    I think you’re missing a zero in there. and then some

  15. blf says

    @4, There was a case very recently here in France — apologies for being unable to locate a reference now (so this is all from memory), but it was this year (2021) — that a child, presumably a young unbaptized baby, was reburied in a village’s cemetery. The child died something like 50(?) years ago, and the local priest at the time refused to bury it in the cemetery. However, recent renovations made it necessary to exhume the child, and so the present-day villagers took up the case and obtained permission to rebury the child in the cemetery. The reburial was apparently attended by thousands (totally swamping the tiny village’s population).

  16. imback says

    This topic is covered in the first chapter “The Way the Spirit Comes to the Bones” of Carl Zimmer’s new book Life’s Edge: The Search for What It Means to Be Alive. This chapter title is from Ecclesiastes 11:5 which in the English Standard Version says “As you do not know the way the spirit comes to the bones in the womb of a woman with child, so you do not know the work of God who makes everything.”

    Zimmer discusses the history of ensoulment and quickening and that it was only in the last century that conception was pressed as the beginning of a life. Zimmer counters:

    The egg arose from cells that divided when the mother was still an embryo. A man makes hundreds of millions of sperm each day, but ultimately they all descend from the fertilized egg that gave rise to his entire body. The flow of life arrives unbroken from the previous generation, and from generations back through the ages. You’d have to canoe up life’s river for billions of years before reaching its headwaters…The actual course of human development makes it impossible to pin one instant as marking the origin of a new human individual. It certainly can’t be the moment that a sperm fuses with an egg.

    Zimmer explains that one reason a person’s origin can’t be the moment that a sperm fuses with an egg is that at that moment the cell actually has 69 chromosomes and it needs to shed 23 and pair up the remaining 46 to have the proper structure for a human individual, which doesn’t really happen until the single cell has already split into two. But even a set of properly structured DNA cannot define a person, since on the one hand, two people who are identical twins have the same one set of DNA, and on the other hand, one person can be a merged fraternal-twin chimera having two different sets of DNA.

  17. chris61 says

    To state the obvious: the lives of every person answering the question began at conception and the vast majority of them understand that had they been aborted prior to birth they wouldn’t be answering that or any other question. Hence the vast majority of people will agree that life begins at conception. Rather than trying to argue that isn’t the right answer it might be more productive to focus on why that isn’t the right question, at least when it comes to abortion.

  18. says

    There is exactly one reference to abortion in the entire Bible, Old Testament and New. It is in Numbers 5, which prescribes a ceremony for inducing abortion in the case of an unfaithful wife. Rather embarrassing, so they never mention it.

  19. ealloc says

    I sometimes suspect that the “life begins at conception” argument is one of the more vulnerable points for anti-choicers; there’s a chance of reaching people by breaking it down, and it’s axiomatic to many people’s philosophy. I managed to convince someone about it on an apologetics forum a long time ago. They came back after months of silence to say the following argument convinced them: (PS, if there are any errors here let me know)
    In which of the following steps you think a new human being comes into existence after sperm + egg meet (the “moment of conception”) and why? Note: A typical human cell has a “diploid, single-chromatid” (2n 1c) set of chromosomes: It has two different versions of each chromosome (2n, one from each parent), and one copy of each version (1c). Let us agree that before step 1 no human exists. The time from step 1 to step 10 is roughly 24 hours, each step takes a few hours.

    .1. The sperm cell (1n 1c) reaches the egg (1n 1c) and they just barely touch.
    2. “key” proteins on the sperm fit into “lock” proteins on the egg, triggering the egg to “wake” from its dormant state.
    3. The sperm and egg’s lipid membranes begin to fuse, until their cytoplasms are connected.
    4. The contents of the sperm cell (including the father’s DNA) enter the egg’s cytoplasm at one end of the egg. The eggs’s (mother’s) DNA moves to the opposite end of the cell.
    5. Separate lipid membranes form around the sperm’s DNA and the egg’s DNA, forming two “pronuclei”. Each pronucleus contains a haploid single-chromatid set (1n 1c), each with DNA from only one parent.
    6. The DNA in each pronucleus duplicates. Each pronucleus is now (1n 2c).
    7. The mother and father’s pronuclei move towards each other to the center of the cell, and the pronuclear membranes dissolve. The (now combined) 2n 2c set of chromosomes floats together in the cell.
    8. The “spindle apparatus” pulls the duplicated chromosome copies apart, one copy to each end of the cell. (2n 1c at each end).
    9. The cell splits in two, forming two cells. Each cell contains a free-floating diploid single-chromatid set (2n 1c) with half DNA from each parent.
    10. The nuclear membrane forms around the chromosomes in each of the two new cells.

    Step 10 (with two cells) is the first time we see a “normal” human cell, that is, a (2n 1c) cell which has a copy of both mother and father’s DNA contained together in a nucleus, which will go through the normal cell cycle.

    For any choice of step, one then points our the absurdity the choice, in defining the previous step is “non-life” while the next one is “life”, since each step is such a tiny mechanical change.

  20. Owlmirror says

    Carl Sagan wrote this essay: The Question of Abortion: A Search for Answers. I realize he was not a biologist, but he certainly seems to be referring to actual biological points.

    I’ve posted it before, but if any biologist responded to it with a critique, I honestly don’t recall seeing it.

    There are comments on the post containing the essay, from anti-abortion partisans.

  21. robro says

    cervantes @ #20 — I read about that passage a couple of months ago as this law was under consideration. That is the only Bible passage that is sometimes cited as being about abortion. While it’s clearly a magic potion and ritual performed by the priest to ferret out the evil adulteress for the wronged husband, whether the potion could induce an abortion is apparently speculative.

  22. anat says

    chris61 @19: There are so many events that could have happened or not to preclude a person from being around to answer said survey, I don’t know why you assign more significance to conception than to any of the rest.

  23. unclefrogy says

    That is methodologically a terrible survey. I’d like to know the details of the question: the summary implies that they were given “options”…a multiple choice question? Was “This question is bullshit” one of the options? I think probably not. Just the idea of putting the question in the form of multiple choices or true/false limits the potential accuracy of the answer.

    very clearly put. I have never have taken a survey or test for that matter that does not have problems in it.
    the question about life and fetus and personhood is so obscure as to be that I can not even form any opinion clearly enough to push it out to everyone.
    as was said above there is an unbroken chain of living organism back to the first life billions of years ago.
    It seems to me that this controversy is rooted in an unscientific even anti-scientific understanding of the world. A strong desire for their folk tales and superstition be true. A reaction to the modern world and reinforced by fear from experience and fanned by charismatic people who also suffer from the contradiction of their beliefs and demonstrable by scientific evidence of the nature of reality. They have little hesitancy to resort to “any means necessary” as judged by them to try to enforce their ideas about reality.

  24. raven says

    Jeez, what a rathole we’re in.

    It’s worse than that.

    At one time long ago, I was sort of proud to be an American. Leader of the free world, staring down the Commie empire, sending humans to the moon, inventing the polio vaccine, and a whole lot more.

    I’m not even embarrassed any more.
    I had no say in where I was born so it isn’t my fault I’m an American.

    These days, I wish I lived somewhere else.

  25. John Morales says


    At one time long ago, I was sort of proud to be an American.

    USAnian. Venezuelans aren’t Americans, apparently.
    Nor are Canadians, Brasilians, Mexican (Estados Unidos Mexicanos!) or any other people in the Americas.

    Only USAnians are Americans, because they’ve snaffled the demonym.

  26. Ian R says

    I have it on the authority of several of my older relatives that life begins at retirement. There’s some possibility that it might be when student loans are paid off, though.

  27. whywhywhy says

    Having gone through Catholic school (same building for 12 years and , no, I was not held back), we would read the Bible and it was full of talk about concubines which is just an obscure way of saying slave-rape. However, the teachers, adults, and kids never seemed to wonder why the multiple wives and multiple slaves went away. At the same time, we would discuss how the traditions of the Church and the Bible guided our morality and were ‘unchanging’. The mental gymnastics needed for this are part of a ‘good’ Catholic education.

    Abortion stances are much like this. The Catholic Church first recognizes a human after birth, defines an age of reason to be around 6 years old, and becoming an adult is around 14 and they have ceremonies associated with each. They do not have funerals for miscarriages and have struggled with what happens to the ‘soul’ of a child if they die after birth and before baptism (thus the invention of purgatory) but do not seem to struggle with what happens to the ‘soul’ of children from miscarriages. Thus they understand very well that human development is a progression. It took a lot of work (mostly by unmarried old white men who understood that the easiest way to get a new church member is to raise one) to get to their anti-abortion and anti-contraception stances in the 20th century. Now the abortion/contraception stance seems to dominate all others within many if not most congregations. On the optimistic side, only one of my six siblings is still Catholic : )

  28. robro says

    John Morales @ #28 — Language is finicky, isn’t it. Perhaps “USians”?

    One wonders if the naming choice might reflect something of the “manifest destiny” ideology that Northern European, Christian landowners from the new nation would someday control the entire hemisphere. There were ideations of annexing Central America to create slave states, which they did in Texas, so why not more. And then there’s the presumptions of the “Monroe Doctrine”.

  29. Russell P says

    I corresponded with Steven Jacobs by email (because he wanted me to sign the legal brief). He uses some unusual language regarding “human”, “human life”, “human being”, “person”, etc. In my email to him, I referred to when a “human being” comes into existence. He did not like this language, and “corrected” me. Here’s what he wrote:

    “Human life” refers to something that is alive and has human DNA. “Humans” (or human beings in your language) refers to organisms with human DNA developing in the human life cycle. This is a distinction your repeated claim that human eggs are humans fails to recognize—if a human entity is not developing in the human life cycle, it is human (adjective) but it is not a human (noun). –Steven Jacobs (11 July 2021)

  30. says

    That’s a terribly biased article from the College Fix (to no one’s surprise). All of this came about simply because Jacobs asked thousands of scientists several questions about when they believe human life begins – questions one respondent referred to as a “trap” and another called “horribly manipulative.” That’s the problem: he’s doing survey research, and he doesn’t know how to design a basic survey to make it impartial. His committee should have failed him, not for his conclusion, but for the sloppy and unprofessional way he arrived at it.

    But hey, he’s got a bright future ahead of him distorting the facts for the Republican party!

  31. says

    I think there’s a reasonable argument to be made that human life begins at birth. Until that point, the fetus just doesn’t have an independent existence, nor does it exhibit many of the basic qualities that are clearly human.
    E.g. Human beings acquire oxygen and expel carbon dioxide by breathing. A fetus doesn’t.
    Human beings eat through their mouths and poop out their assholes. A fetus doesn’t.
    Human beings perceive their world, form opinions about it, and act within it. A fetus doesn’t.

    Note that if a human being (i.e. after birth) ceases to exhibit any of these qualities, it’s a major warning sign that they may be dead or dying. That implies that these are quite fundamental characteristics. If a given quality is essential for a human being, yet a fetus doesn’t ever have this quality, then how is the fetus human?

    I’m not trying to argue that this is the right answer. There’s no objectively right answer, since the question depends so much on what you mean by “human”. However, I think this argument holds up at least as well as some I’ve heard.

  32. wzrd1 says

    ‘“Human life” refers to something that is alive and has human DNA.’

    Huh, Henrietta Lacks is both immortal and a very, very large human, given the prominence of HeLa cell cultures all around the planet and his idiotic daffynition.
    Note how both statements agree with his deficient argument, in that there is no self-sustaining life support mentioned for either. His argument simply turns women into culture incubators.